A variety of products and articles, including, for example, medical instruments, devices, and equipment, must be sterilized prior to use to prevent bio-contamination of a wound site, a sample, an organism, or the like. A number of sterilization processes are used which involve contacting the product or article with a sterilant. Examples of such sterilants include steam, ethylene oxide, hydrogen peroxide, and the like. Steam sterilization is widely used, at least in part because multiple batches of articles can be subjected to sterilization conditions during a 24 hour period using a single steam sterilizer.
Monitoring for conditions sufficient for sterilization is generally carried out by placing an appropriate sterilization indicator along with the product and/or article to be sterilized within a sterilization chamber. A variety of sterilization indicators, including chemical and biological indicators, are known and used for this purpose. Chemical indicators offer an advantage in that they can be read immediately at the end of a sterilization process. Steam sterilization indicator compositions that have been used include a polyvalent metal compound, such as lead carbonate, and sulfur. Such indicators turn to brown or black when their color is fully developed by a steam sterilization condition.
Because of environmental concerns, lead compounds have been and continue to be replaced by other polyvalent metal compounds. In one example, bismuth has been proposed to replace lead in certain steam sterilization indicator compositions as described in U.S. Pat. No. 5,916,816 (Read) wherein, for example, bismuth subcarbonate was used.
Accordingly, there is a continuing need for lead-free chemical indicators which can indicate that a steam sterilization process condition has been met.